1. Field of the Invention
The present invention relates to reinforced pressure-sensitive adhesive tapes, and to a method and apparatus for making these tapes.
2. Description of the Prior Art
Reinforced tapes, also known as filament tapes, generally comprise a backing having adhered to one major surface thereof a plurality of yarns, which comprise a multiplicity of glass or synthetic polymeric filaments, by means of an adhesive. Alternatively, the yarns can be replaced by individual filaments. Typically, a layer of pressure-sensitive adhesive is then applied over the yarn- or filament-bearing surface of the tape. Filament tapes can be made by applying continuous filaments or yarns drawn from warp beams or spools to a substrate, e.g., a film or paper backing. U.S. Pat. No. 2,750,315 discloses a process in which a film or paper backing is first coated with an adhesive solution and then dried sufficiently to remove the bulk of the solvent. Then, synthetic polymeric yarns are laminated to the backing. The yarn-bearing backing is then coated with a second adhesive solution and then dried again. The finished tape is then wound into a jumbo roll, slit, and wound into tape rolls in a conventional manner. This method is also applicable to untwisted mono-fiber filaments. During all of these steps, many problems can occur. One of the most common problems is breakage of the filaments from the warp beams during the lamination step. Much time must be spent during initial set-up to thread the individual yarns from the warp beam into the yarn combs in order to provide proper alignment of yarns during the laminating step. The processing of hundreds of yarns, which are very fragile, is difficult. Selection of optimum process conditions, such as yarn tension, adhesive coating, and lamination, is critical to minimize waste and rework. Another problem is compatibility of the adhesive systems with the yarns of the tape. Although the adhesive does surround the individual yarns which are comprised of bundles of filaments, it does not coat each individual filament. This can result in poor bond between the adhesive and the surface of the filament.
U.S. Pat. No. 4,592,938 discloses a method for producing an internally reinforced film web through coextrusion of two polymeric materials. Tensile strength is enhanced by means of flat reinforcing strips embedded within the matrix material of the film web in the longitudinal direction of the film web. The primary use of the film is to reinforce plastic bags and components thereof.
U.S. Pat. No. 4,536,362 discloses a process for making a plastic film having longitudinal ribs by extrusion of a resin through a pair of spaced die lips. One of the die lips is provided with slots which runs at an angle to the direction of flow of resin across the die lips. Impurities in the resin are collected by and retained in the slots provided in one of the die lips. This occurs because of the shear stress field created by the arrangement of the slots during the extrusion process; consequently, all the impurities in the resin are collected and contained in the thickened rib portion of the film, thus reducing the deleterious effects of the impurities upon film performance.
U.S. Pat. No. 4,454,192 discloses a process of making a pressure-sensitive sheet adhesive tape by burying a plurality of artificial filament yarns in the sheet and then embedding the filament yarns with a suitable adhesive. The artificial yarns are buried in one side of the sheet so that at least half of the sections of filament yarns are exposed to permit embedding in the adhesive layer. This procedure is subject to many of the same mechanical processing problems which involve application of yarns onto a tape backing, e.g., yarn breakage, loss of equipment run time, and quality of the material.
Although filament tapes are extremely useful, the cost of making them is high because of the high cost of filaments and the high cost of processing. In order to reduce the cost of making filament-reinforced tapes, some manufacturers have resorted to reducing the number of filaments adhered to the backing. However, this expedient reduces the tear strength of the tape.
While high quality filament-reinforced tapes are known to have an extremely high level of tear strength, they are generally used only once, thus making their use costly to the consumer. It is therefore desired to have a tape having a reasonably high level of tear strength, but at a much lower cost than that of high quality filament-reinforced tapes.